The truck runs good but when you press on the gas pedal it almost seems as though it is delayed, like the truck is being flooded with gasoline and so it takes a moment for it to process, or that it takes a second for the truck to realize that i've pressed the gas down. I don't know if this is normal with older trucks? and also in the 35-40 mph range and at low rpms the truck will buck as if i were pressing and letting go of the gas pedal multiple times even though im keeping it at a constant pressure, what could this be?

Tried-
Fuel Filter
Spark Plugs
Coolant temp senor
Thermometer
Alternator
has new headers (02 sensor)